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Programming Tips
TVP4020
Programmers Reference Manual
146
7.5.2
Triple Buffering
Most 3D systems support double buffering where one frame is displayed
while the next frame is being drawn. To avoid display artifacts, the
change between old and new buffers must happen during a vertical
frame blank, but this imposes a granularity on the frame rate. If a scene
takes slightly longer than one frame period to draw, it has to wait for
another frame before it can display so the frame rate halves.
If three buffers are used, the quantization is removed and the system
can continue to draw at maximum rate.
7.6
Overlays
Overlays are only available with the 5551 color format in a 32 bit pixel.
The P
ERMEDIA
5551 color formats copy the data into both 16 bit halves of
the 32 bit pixel. The writemask is used to write either the upper or lower
half to memory.
The RAMDAC can be programmed to display a 16 bit pixel from either
the upper or lower half of the 32 bit word; which one is displayed is set
by bit 31. Bit 31 corresponds to the alpha bit of the 16 bit pixel, and this
can be forced to either 1 or 0 by the Color Format unit.
When drawing to the underlay (or main image) set the Color Format unit
to force the alpha to zero, set the writemask to allow writes to the lower
half of the word. When drawing to the overlay set the Color Format unit
to force the alpha value to 1 and writemask to allow writes to the upper
half of the word.
If the RAMDAC is set into the appropriate mode, pixels in the overlay
half of the word will be drawn where alpha is 1 in the overlay and from
the main image where it is zero in the overlay.
7.7
Memory Organization
The amount of memory available to P
ERMEDIA
depends on the board it is
fitted to. The most efficient way to allocate memory will depend on the
needs of the system, but in general the display should be allocated at
one end of the SGRAM and the localbuffer at the other end. This leaves
a region between the two buffers in which textures can be stored. For
optimal performance, each buffer (front color, back color, texture and
depth) should reside in separate memory banks. Memory is organized
as follows:
memory
bank
size per
Содержание TVP4020 PERMEDIA 2
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Страница 47: ...Memory I O and Organization TVP4020 Programmers Reference Manual 38 Texture address TextureBaseAddress T W S ...
Страница 284: ...TVP4020 Programmers Reference Manual A Gouraud Shaded Triangle 275 ...
Страница 292: ...TVP4020 Programmers Reference Manual Register Tables 283 ...
Страница 314: ...TVP4020 Programmers Reference Manual Index 305 ...
Страница 315: ...Index TVP4020 Programmers Reference Manual 306 Index ...
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